High leakage transformer and gaseous discharge lamp circuit regulated by such transformer



y 9. 1968 A. E. FEINBERG 3,392,310

I'I'KGH LEAKAGE TRANSFORMER AND GASEOUS DISCHARGE LAMP CIRCUIT REGULATEDBY SUCH TRANSFORMER Filed May 51, 1955 (8 L/l/l FIG. 6

nvmvron A! an E Fe/hberg United States Patent HIGH LEAKAGE TRANSFORMERAND GASEOUS DISCHARGE LAMP CIRCUIT REGULATED BY SUCH TRANSFORMER AlbertE. Feinberg, Chicago, Ill., assignor to Advance Transformer Co.,Chicago, 111., a corporation of Illinois Filed May 31, 1955, Ser. No.512,034 23 Claims. (Cl. 315--278) This invention relates totransformers, particularly a transformer for a gaseous discharge tube ortubes which are connected in a circuit such that a coil of thetransformer takes a leading current. The present invention is moreparticularly concerned with means for controlling the leakage reactanceof a leading secondary coil of a transformer of the type commonly usedfor fluorescent lamps, or the like.

Lighting circuits for fluorescent lamps commonly utilize what is knownas a high leakage reactance transformer. This consists of a primary andone or more secondaries, frequently with a magnetic shunt between thesecondaries, and, in addition means for providing a loose couplingbetween the secondaries and the primary. This loose coupling may beobtained by mechanical spacing between the primary and the secondary orby a magnetic shunt between them, with an air gap. The secondary may beelectrically insulated from the primary or may be connected therewith instep-up auto-transformer relationship. The operating current of thegaseous discharge tube or tubes is supplied through the secondary, andthe regulation of the secondary current is in a measure dependent uponthe leakage reactance. The present invention relates to the means forcontrolling the leakage reactance of a secondary which supplies currentto a gaseous discharge tube over a circuit in which the current isessentially leading with respect to the primary voltage.

In the case of a transformer that supplies current to one or moregaseous discharge units through a circuit in which the current throughthe unit is essentially a leading current, it has been found necessaryto place an air gap in the path of that magnetic flux which is common toboth the primary and the secondary windings, in order to preventsaturation of the secondary winding. This is illustrated, by way ofexample, in the patent to Berger, No. 2,461,957. The vector relationshipindicates that the voltage drop across the secondary coil in a leadinghigh reactance ballast is greater than the initial open circuit voltageaoross this coil. As a result, there is a tendency for the currentthrough this secondary to increase, causing a saturation of the core atthe secondary. As the current increases through the secondary theleakage reactance decreases. This changes the total impedance which isequal to the capacity reactance minus the inductive reactance. The dropin impedance causes still further increase of the current flow whichcauses a further drop in impedance and again increases the current flow.This continues until the iron is magnetically saturated. When the ironis operated in a saturated condition the current wave shape through thelamp is highly peaked giving a very poor light output and decreasing thelife of the lamp.

As set forth in the above-mentioned Berger patent, a gap in the magneticcircuit of the flux that is common to the primary and secondary willsubstantially diminish this saturation and the wave distortion, in thatthe gap introduces a high reluctance of a fixed value in series with thereluctance of the iron circuit, which latter reluctance varies atdifferent values of flux density.

Commercial transformers of the type with which the present invention areconcerned are generally made of a long and narrow construction. Thisshape is necessitated by either or both of two considerations. One is,it is neces- 3,392,310 Patented July 9, 1968 sary to conform the ballastor transformer to the shape of the channels that are provided in thelighting fixtures in which the transformers are to be mounted, whichchannels are very narrow. The other consideration is that in order tomaintain an economic ratio between the copper and the iron of thetransformer the secondary turns must be of small diameter. Theelectrical conditions that must be satisfied by the transformer requirethe use of many turns of wire, and fix the size of the wire, whichtherefore results in a comparatively long secondary. This isparticularly true where the transformer is to supply operating currentto two 72 inch or 96 inch fluorescent lamps, commonly known as the rapidstart type, and which are economically operated two lamps in series. Ihave found that in the case of a transformer having a very longsecondary which supplies a current that is leading with respect to theprimary voltage, the provision of an air gap in the secondary leakageflux path is insuflicient to prevent saturation of the core by thesecondary leakage flux. This is probably due to the fact that the longerthe secondary the greater is the possible magneto-motive force that isresponsible for the secondary leakage flux. Therefore, in the case of along secondary, portions of the secondary are frequently so remote fromthe air gap that the magneto-motive force which produces the secondaryleakage flux is sufficient to cause saturation of the magnetic structureof the transformer in the region of that flux.

I have found that by distributing the air gap so that it is in the formof a number of spaced apart gaps in series and at various locations withrespect to the secondary that carries the leading current, the differentones of the gaps can introduce sufficient reluctance in any of thepossible leakage flux paths so that saturation of the core is prevented.

Reference may now be had more particularly to the drawings which showthe principles of the present invention applied to various types oftransformer cores which are otherwise of standard construction.

In the drawings:

FIG. 1 is a sectional view of a transformer of a two lamp fluorescentballast having a magnetic construction in accordance with thisinvention;

FIG. 2 is a fragmentary sectional view taken along the line 22 of FIG.1;

FIG. 3 is a circuit diagram illustrating one typical connection for thewindings of a ballast of the present invention; and

FIGS. 4, 5 and 6 are views similar to FIG. 1 and showing the presentinvention as applied to different types of transformer cores.

The transformer of FIG. 1 includes a primary coil 1 and a secondary coil2 mounted on a magnetic core 3 which is assembled with a pair of similaryokes 44. The core and the yokes each comprises a similar number oftransformer steel laminations stacked together and held in assembledrelation in any desired manner. In the transformer illustrated in FIG.1, the core and the yokes each comprises a stack of approximately fiftylaminations having an overall thickness of the order of 1.25 inches.Each yoke 4 includes a pair of end legs 6-7 and an intermediate shunt 8,all joined by a longitudinally extending side 9. The two sets ofpreassembled yokes 4 are assembled with the preassembled core 3, onwhich the primary and seconda y have been mounted, to formthetransformer, and are held in assembled relationship in any desiredmanner. The shunts 8 extend almost up to the core 3 but leave air gapsat 12 which are of a height of the order of .04 inch from the core tothe yoke. The core 3, in one construction, was one inch wide andapproximately 78 inches long. The Width of the iron structure of FIG. 1was approximately 2.9 inches. Each of the longitudinal sides 9 wasapproximately /2 inch wide as were each of the legs 6, 7 and 8. Theprimary and secondary coils extend through windows formed between thecentral core 3 and the yokes 44, and bounded by the shunt 8 and the endleg 6 in one case and the end leg 7 in the other. The iron corestructure thus far described is a conventional structure known as ashell type structure.

In order to effect economies in the amount of copper used, it iscustomary to make the coils 1 and 2 of an appreciably greater axiallength, that is, length in a direction parallel to the core 3, thantheir thickness in a direction from the core 3 to the yoke 4. In view ofthe size of the wire used and the number of turns required, it follows,therefore, that the coils, particularly the secondary coil, is ofappreciable axial length. In one design, the primary had 350 turns ofNo. 20 copper wire and was 2 /2 inches long and with an outside diameterof the order of 1.9 inches, whereas the secondary had 2020 turns of No.22 copper wire, was of a length of approximately 3% inches and with thesame outside and inside diameters as was the primary.

The core 3 has a series of air gaps 15, 16, 17 therethrough at theportion thereof that is surrounded by the secondary 2. Each of said airgaps 151617 is of a width in a direction extending axially of the core3, of the order of .05 inch and of a length extending substantially thefull width of each core lamination 3, leaving only a small bridge atopposite ends of the air gap for maintaining the mechanical unity of theportions of the core 3 on opposite sides of the air gap. The distancefrom the air gap 16 to the primary 1 is, as may be seen from FIGURES 1and 2, more than 30% of the length of the secondary. Also, the length ofthe secondary coil is greater than 1.5 times its diameter. The purposeof the air gaps 15-1617 is to introduce distributed reluctance in thepath of the secondary leakage flux for the purpose of preventingsaturation of the magnetic structure by the secondary leak age flux.

FIG. 3 shows one standard circuit for the primary and secondary ofFIG. 1. In this circuit, the primary 1 is connected across a line thatsupplies 120 volts 60 cycle current. The secondary 2 is connected instep-up auto-transformer relationship with the primary 1 and, in serieswith a condenser 25 (approximately 3 microfarads), supplies starting andoperating current to two fluorescent lamps, indicated at 27 and 28, thatare connected in series, the lamp 28 being shunted by a condenser 29.This is a conventional rapid start circuit wherein the condenser 29by-passes the lamp 28 to supply starting voltage to the lamp 27. Thelamps are conventional 72" T-l2 or 96" T-12 gaseous dischargefluorescent lamps rated at 100 watts and operating with 800 milliamperesto 1 ampere. These lamps, operating two in series, require a total opencircuit voltage of 530 volts. After the lamp 27 has started, the voltagethereacross drops, and there is then sufficient voltage to start thelamp 28 which then operates in series with the lamp 27.

The transformer of FIG. 1 together with the condensers, as illustratedin FIG. 3, is placed into a casing 20, which is generally of iron orsteel, and in which the transformer fits snugly. The free space withinthe casing is filled with an insulating compound of tar-like consistencywhich excludes all air from around the transformer. The reluctance ofthe air gaps 15-1617 reduces the flow of secondary leakage flux throughthe casing and thus reduces objections that are otherwise inherent insuch a structure.

By placing two or more air gaps 15, 16 and 17 in the core of thesecondary 2 it is possible to control the leakage reactance of thesecondary so that the resulting current is fairly close to a sine wave.It is believed that the theoretical reason for the success of amultiplicity of relatively small air gaps as against the use of onelarge air gap lies in the ratios between the width and the crosssectional area of the air gap on the one hand, and the width and thecross sectional area of the window space between the core and the shellthat is occupied by the secondary 2. In the transformer hereinabovedescribed, this space was .45 inch, and the approximate length of thewire portion of the secondary coil was slightly over three inches. Thereluctance of any air gap is proportional to the length of the gapdivided by its cross sectional area. Since the height of the stack isthe same relative to any air gap in the core and the window spaceitself, the relucance of the window space overall will be inverselyproportional to the length of the window, and the relucance of the gapin the core will be inversely proportional to the width of the core.Therefore, if, for example, the air gap at the end of the core isapproximately .05 inch and the total window length at the secondary,figuring both sides of the core, is six inches, the reluctance of thewindows as a shunting path will have an area in the ratio of l to 6 forthe end gap compared to the reluctance of the windows, if a single endlocated air gap were used. Therefore, taking into consideration thelength of the gap as being .05 inch for such end gap, its reluctancewould be in the ratio of .05 to 1. The reluctance of the window would beof the ratio of .45 to 6, so that it can be seen that there is hardly a2 to 1 ratio in the reluctance of the window itself as compared to thereluctance of the air gap. Therefore, considering that themagneto-motive force of the long coil would tend to send flux into theair gap, and if it were limited only by the effect of an end air gap,the leakage through the window becomes quite a factor and is sufficietlylarge to permit saturation of the secondary despite any increase thatmay be made in the end air gap. However, if the air gaps are distributedalong the length of the long secondary core, as illustrated in FIG. 1,and are magnetically in series, they will thereby considerably limit theflow of secondary leakage flux to any considerable portion of the core 3and thence across the windows themselves. This thereby controls thesecondary leakage flux to prevent saturation of the secondary by theleakage flux.

The ballast of the present invention is also quieter in its operationdue to the fact that the distributive air gaps 15, 16 and 17 reduce theamount of leakage flux that can flow through the casing 20 and therebyeliminate or substantially reduce the hum that would otherwise be causedby a large secondary leakage flux flowing through the casing 20.

In the ballast of FIG. 1, the condensers 25 and 29 are housed within thecasing 20.

The principles of the present invention are applicable to other types oftransformers for gaseous discharge tubes wherein there is a secondarythat takes a leading current and wherein the length of the secondarycreates the saturation problem hereinabove set forth. In FIG. 4 there isillustrated a structure wherein the principles of the present inventionare applied to a transformer core of the type shown in the patent toBrooks, No. 2,562,693, being particularly useful if the ballast requiresa leading secondary coil 37 of appreciable length. The core of theballast of FIG. 4 is identical with that shown in the Brooks Patent2,562,693 and to which reference is made for a more completedescription. This core differs from that of the Brooks patent only inthat the length of the space for the leading secondary 37 isproportionately longer, and by the provision of two air gaps 15 and 16which extend across the core 35 in the same manner as in FIG. 1heretofore described. These'two air gaps are in addition to the bridgedair gap 47 the function of which is described in the Brooks patent,which air gap 47 has been, optionally, substituted for the air gap 17 ofFIG. 1 of this application.

In the structure of FIG. 4 the primary is indicated at 38. A secondary36 is connected in auto-transformer relationship with the primary andsupplies a lagging current to a gaseous discharge device. A secondary 37is connected in step-up auto-transformer relationship with the primaryand is connected in series with a condenser to provide a leading currentfor a gaseous discharge device, as shown in the Brooks patent, or toprovide a leading current for two series connected gaseous dischargedevices, as illustrated in FIG. 3 of this application.

The principles of the present invention are applicable alike to coretype transformers as well as shell type. To that effect, there isillustrated in FIG. 5 the core type transformer of Berger Patent No.2,461,957 in which the end air gap of that patent has been omitted andin lieu thereof the core which comprises two stacks of L-shapedlaminations has been provided with distributed air gaps 15a, 16a and 17ain one stack thereof and 15b, 16b and 17b in the other stack theerof,these air gaps being identical with the air gaps 15, 16 and 17heretofore described. In this ballast, the coils 6a and 7a are connectedin series by a conductor 50 and together constitutes a primary. Thecoils 8a and 9a are connected in series by a conductor 51 and togetherare connected in auto-transformer relationship with the primary andsupply lagging current to a gaseous discharge tube. The coils 11a and12a are connected in series by a conductor 52 and together constitute asecondary which is connected in step-up auto-transformer relationshipwith the primary and in series with a condenser 13a and supplies leadingcurrent to a lamp, as shown in the Berger patent, or to two or morelamps as shown in FIG. 3 hereof. The necessary loose coupling betweenthe primary and the leading secondary 11a-12a is obtained by adequatelyspacing the secondary from the primary, or by a shunt and air gapbetween them, such as the shunt 8 and air gap 12 of FIG. 1.

In FIG. 6 there is illustrated a transformer such as shown in FIG. 1 ofthe patent to Feinberg, No. 2,683,243, to which patent reference is madefor a more complete description thereof. The transformer of FIG. 6differs from that of Patent 2,683,243 in that here there have been addedthe air gaps 15c and 160 which correspond to the air gaps 15 and 16 ofFIG. 1 hereof. The end air gap 22c which corresponds to the air gap 22of Patent 2,683,243 may be used in lieu of the air gap 17 of FIG. 1. Inthis ballast S and S; are secondaries, and between them is a primary Pwhich may combine a primary and a third secondary. The coils S P and Scorrespond to the coils bearing the same reference numerals in Patent2,683,243 to which reference is here made. This ballast is connected incircuit the same as illustrated in the above referred to Feinberg patentto which reference may be had, for a more complete description.

In the descriptions above given of the structures of FIGS. 4, 5 and 6, Ihave omitted detailed descriptions of those portions of the respectiveballasts that have not been changed by the present invention, andreference is here made to the disclosure in the corresponding patentsabove referred to for the details of construction of the respectiveballasts or transformers of FIGS. 4, 5 and 6 just as though thosedetails were incorporated in the present specification.

The transformers of FIGS. 4, 5 and 6 together with their associatedcondensers are enclosed in casings such as the casing 20 of FIGS. 1 or2. From the above specification it is apparent that the principles ofthe present invention are applicable to a wide variety of transformers.The advantages of the forced core construction of FIG. 8 or thesemi-forced core construction of FIG. 5 may be utilized in connectionwith the principles of the present invention.

In compliance with the requirements of the patent statutes I have hereshown and described a preferred embodiment of my invention. It is,however, to be understood that the invention is not limited to theprecise construction here shown, the same being merely illustrative ofthe principles of the invention. What I consider new and desire tosecure by Letters Patent is:

1. Apparatus for supplying a leading current to a gaseous dischargedevice comprising primary and secondary coils and an iron core couplingthe 'two, the secondary being of an axial length greater than 1.5 timesits diameter, said core having a magnetic portion extending lengthwiseof the secondary and adjacent thereto and constituting a part of theleakage flux path of the secondary and having non-magnetic gaps inseries with one another and spaced from one another lengthwise of thesecondary by an amount which is a substantial fractional part of theaxial length of the secondary, the width of the magnetic material leftin the primary flux path of the magnetic portion at each gap being aminor fractional part of the distance between adjacent gaps.

2. An apparatus as defined in claim 1 wherein said magnetic portion withits non-magnetic gaps is in the path of the primary magnetizing flux andoutside of the primary leakage flux.

3. An apparatus as defined in claim 1 wherein the portion of the corethat includes the non-magnetic gaps is surrounded by the secondary.

4. An apparatus as defined in claim 1 wherein there is a condenser inseries with the secondary coil and of a capacity sufiicient to cause thecurrent flowing through the secondary to be leading with respect to theprimary voltage.

5. An apparatus as defined in claim 2 wherein each of the non-magneticgaps is bridged by a magnetic portion of the core.

6. An apparatus as defined in claim 3 wherein there is a magnetic casingfor said apparatus, the casing being closely adjacent to the secondaryand, together with the magnetic portion and the series air gaps,constitutes a part of the path for secondary leakage flux.

7. Apparatus as defined in claim 6 wherein there is a condenser in thecasing and in series with the secondary coil and of a capacitysufficient to cause the current flowing through the secondary to beleading with respect to the primary voltage.

8. Apparatus for connection to an alternating current source of fixedfrequency for supplying leading current to a gaseous discharge devicecomprising primary and secondary coils, an iron core coupling the two,the secondary coil being of greater length than 1.5 times its diameter,said core having a plurality of high reluctance portions in series withone another in the path of the primary magnetizing flux, said portionsbeing also in the path of the secondary leakage flux that links all ofthe secondary turns and being spaced from one another in a directionaxially of the secondary so that such secondary leakage flux that linksonly a fractional portion of the turns of the secondary will passthrough less than all of the high reluctance portions, the distancebetween adjacent high reluctance portions being greater than the radialthickness of the secondary.

9. Apparatus as defined in claim 8 wherein there is a condenser inseries with the secondary and of a greater capacity reactance at thefrequency of the source than the inductive reactance, at said frequency,of said secondary and the load connected thereto.

10. In combination with two series connected gaseous discharge devices,a condenser shunting one of the devices, means forming a leading circuitwith said devices, said means including a high reactance transformerhaving an output voltage less than the sum of the starting voltages ofthe two devices and greater than the starting voltage of each device,said transformer including a primary coil and a secondary coil in axialalignment with one another and spaced axially of one another, so thatsuccessive portions of the secondary are progressively further from theprimary and the secondary is outside of the path of the primary leakageflux, an iron core coupling the primary and secondary coils, thesecondary being of an axial length greater than its diameter, said corehaving a plurality of high reluctance portions in series with oneanother in the path of the primary mag- 7 netizing flux and also in thepath of the secondary leakage flux that links all of the secondary turnsand being spaced from one another in a direction axially of thesecondary so that such secondary leakage flux that links only afractional portion of the secondary will pass through less than all ofthe high reluctance portions, the distance between adjacent highreluctance portions being greater than the radial thickness of thesecondary, the primary and the secondary being loosely coupled andconnected in step-up auto-transformer relationship, a condenser inseries with the secondary and in series with the circuit including thetwo series-connected gaseous discharge devices, said condenser beingofgreater capacity reactance at the operating frequency of the apparatusthan inductive reactance of the circuit that includes the secondary, sothat the secondary load current is a leading current, the firstmentioned condenser being of a capacity substantially smaller than thecapacity of the second mentioned condenser and constituting a by-passaround one of the devices for providingsubstantially the entire voltageof the transformer to be applied to the other device to start it,whereupon the second device will then start.

11. A high reactance ballast transformer comprising a shell typemagnetic core, having an elongated central-core leg and a pair of yokecore legs defining coil receiving windows with said central core leg, aprimary winding and a secondary winding arranged on side-by-sideportions of said central core leg within said windows, said central coreleg having a pair of spaced transverse slots forming bridged-gaps in themagnetic circuit of said secondary winding, one of said bridged-gapsbeing no more than 20% of the length of the secondary winding away fromsaid primary winding, and the other bridged-gap being no less than 30%of the length of said secondary winding away from said primary winding.

12. The high reactance ballast transformer of claim 11 wherein saidprimary and secondary windings are connected in autotransformerrelationship.

13. A high reactance ballast transformer comprising a shell typemagnetic core having an elongated central core leg and a pair of yokecore legs defining coil receiving windows with said central core leg, aprimary winding and a secondary winding arranged on side-by-sideportions of said central core leg within said windows, said central coreleg having a pair of spaced transverse slots forming bridged-gaps in themagnetic circuit of said secondary winding, one of said bridged gapsbeing proximate to said primary winding.

14. The high reactance ballast transformer of claim 13 wherein the otherbridged-gap is located remote from said primary winding.

15. A high reactance ballast transformer comprising a shell typemagnetic core having an elongated central core leg and a pair of yokecore legs defining coil receiving windows with said central core leg, aprimary winding and a secondary winding arranged on side-byside portionsof said central core leg within said windows, said central core leghaving a pair of spaced transverse slots forming bridged-gaps therein,one of said slots being located essentially in the magnetic leakage fluxcircuit of said secondary winding only and the other of saidbridged-gaps being located adjacent to that end of the secondary windingthat is closer to the primary winding.

16. Ballast apparatus for starting and operating fluorescent lampscomprising a high reactance transformer including a shell type magneticcore having an elongated central core leg and a pair of elongated yokecore legs defining coil receiving windows with said central core legs, aprimary winding and a secondary winding arranged on side-by-sideportions of said central core leg within said windows, a capacitorconnected in series with said secondary winding for connection in serieswith a fluorescent lamp across said primary winding, and said centralcore leg having a pair of spaced transverse slots forming bridged-gapstherein, one of said bridged-gaps assaaa o being located essentially inthe magnetic circuit of the leakage flux of only 'said secondaryWinding, and the other bridged-gap being closed adjacent to that end ofthe secondary winding that is closer to the primary windmg.

17. Apparatus for igniting and operating gaseous discharge means from asource of alternating 'voltagewhich comprises an iron core transformerincluding an elongated flux conductive element, a primary winding and asecondary winding each coaxially mounted on a different portion of saidelementand coupled relative to one another to provide leakage reactancein the. secondary winding during operation of said apparatus, saidprimary winding being adapted to be connected to said source, acapacitive load circuit including gaseous discharge means connected withsaid secondary winding to have the current of said secondary windingflowing therein of leading character, and means for limiting thesecondary leakage flux comprising a plurality of spaced apart reductionsof area of said portion of said element upon which said secondarywinding is mounted of dimensions to provide localized reduced coreportions of non-linear permeability confined between the ends of saidsecondary winding.

18. In apparatus for igniting, and operating gaseous discharge meanswherein said apparatus includes: terminals for connecting the apparatusto a source of alternating voltage, an iron core transformer having aflux conductive element, primary and secondary windings each coaxiallymounted on a different portion of said element and said windings beingloosely coupled one with the other, said primary winding being adaptedto be connected to the said source, and a capacitive load circuitincluding said gaseous discharge means connected to said secondarywinding to have the current of said winding flowing therein of a leadingcharacter; the improvement consisting of means for substantiallylimiting the secondary leakage flux comprising: a substantial reductionof cross-sectional area in said flux conductive element at a pluralityof spaced apart locations in the portion of said element upon which saidsecondary winding is mounted, said reduced areas being each ofdimensions to provide a localized reduced core portion of non-linearpermeability entirely confined between the ends of said secondarywinding.

19. A high reactance ballast transformer comprising a shell typemagnetic core having an elongated central core leg and a pair of yokecore legs defining coil receiving windows with said central core leg, aprimary winding and a secondary winding arranged on side-by-sideportions of said central core leg within said windows, said central coreleg having a pair of spaced transverse slots forming bridged-gaps in themagnetic circuit of the leakage flux of said secondary winding, thedistance between said slots being in excess of half the length of saidsecondary winding, and one of said gaps being adjacent to that end ofthe secondary winding which is closer to the primary winding.

20. A ballast as set forth in claim 16 in which one bridged-gap in thesecondary leakage flux circuit is located no less than 30% of the lengthof said secondary winding away from said primary winding, and the otherbridged-gap is located adjacent to that end of the secondary Windingwhich is closer to said primary winding.

21. Ballast apparatus for starting and operating fluorescent lampscomprising a high reactance transformer including a shell type magneticcore having an elongated central core leg and a pair of elongated yokecore legs defining coil receiving windows with said central core legs, aprimary winding and a secondary winding arranged on side-by-sideportions of said central core leg within said windows, means forming aleading current circuit including a capacitor and said secondary windingand at least one fluorescent lamp and said primary winding all inseries, and said central core leg having a pair of spaced transverseslots forming bridged-gaps therein, one of said bridged-gaps beinglocated essentially in the magnetic circuit of the leakage flux of onlysaid secondary winding, and the other bridged-gap being located atsubstantially that end of the secondary winding that is closer to theprimary winding.

22. A high reactance ballast transformer comprising a shell typemagnetic core having an elongated central core leg and a pair of yokecore legs defining coil receiving windows with said central core leg, aprimary winding and a secondary winding arranged on side-by-sideportions of said central core leg within said windows, said central coreleg having first transverse slot means forming at least one bridged-gapin the magnetic circuit of the secondary winding adjacent that end ofthe secondary Winding which is closer to the primary winding and havingsecond transverse slot means forming additional bridged-gaps in themagnetic circuit of said secondary winding, said additional bridged-gapsbeing spaced from the first mentioned gap in the direction towards theopposite end of the secondary winding and providing a combined corerestriction greater than the core restriction of said first mentionedgap.

23. Ballast apparatus for starting and operating fluorescent lampscomprising a high reactance transformer including a shell type magneticcore having an elongated central core leg and a pair of elongated yokecore legs defining coil receiving windows with said central core legs, aprimary winding and a secondary winding arranged on side-by-sideportions of said central core leg within said windows, a capacitorconnected in series with said secondary winding for connection in serieswith a fluorescent lamp across said primary winding, and said centralUNITED STATES PATENTS 1,859,115 5/1932 Summers 336178 2,432,343 12/1947Short 336-165 X 2,470,460 5/ 1949 Bird 323--6O 2,473,420 6/1949 Freeman323-48 2,473,746 6/1949 Freeman 336- 2,553,591 5/1951 Kronmiller 336- X2,578,395 12/1951 Brooks 32360 X 2,629,072 2/ 3 Nathanson.

FOREIGN PATENTS 72,223 6/ 1947 Norway.

JAMES W. LAWRENCE, Primary Examiner.

LEO QUACKENBUSH, RALPH R. YOUNG, MILTON O. HIRSHFIELD, RALPH G. NILSON,GEORGE N. WESTBY, Examiners.

A. C. MARMOR, R. C. SIMS, R. M. TAYLOR, C. R.

CAMPBELL, Assistant Examiners.

Patent No 3,392,310

' length of the secondary winding away from" UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION July 9, 1968 Albert E. Feinberg It iscertified that error appears in the above identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 7, lines 31 and 32, cancel "no more than 20% of the to that endof the secondary winding which is closest to Column 8, line 3, "closed"should read located Signed and sealed this 25th day of November 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer and insert adj acen'

1. APPARATUS FOR SUPPLYING A LEADING CURRENT TO A GASEOUS DISCHARGEDEVICE COMPRISING PRIMARY AND SECONARY COILS AND AN IRON CORE COUPLINGTHE TWO, THE SECONDARY BEAING OF AN AXIAL LENGTH GREATER THAN 1.5 TIMESITS DIAMETER, SAID CORE HAVING A MAGNETIC PORTION EXTENDING LENGTHWISEOF THE SECONDARY AND ADJACENT THERETO AND CONSTITUTING A PART OF THELEAKAGE FLUX PATH OF THE SECONDARY AND HAVING NON-MAGNETIC GAPS INSERIES WITH ONE ANOTHER AND SPACED FROM ONE ANOTHER LENGTHWISE OF THESECONDARY BY AN AMOUNT WHICH IS A SUBSTANTIAL FRACTIONAL PART OF THEAXIAL LENGTH OF THE SECONDARY, THE WIDTH OF THE MAGNETIC MATERIAL LEFTIN THE PRIMARY FLUX PATH OF THE MAGNETIC PORTION AT EACH GAP BEING AMINOR FRACTIONAL PART OF THE DISTANCE BETWEEN ADJACENT GAPS.